1. Field of the Invention
The invention generally relates to an optical film and a light source module using the optical film, and more particularly, to a brightness enhancement film (BEF) and a backlight module using the BEF.
2. Description of Related Art
Along with the development of display technology, flat panel display has become the main stream of display to take place of conventional, thick and heavy cathode ray tube (CRT). In flat panel display, liquid crystal display (LCD) is popular with people, and widely used. The LCD includes a liquid crystal panel and a backlight module. The liquid crystal panel may not emit light, and is used to determine light transmission rate, so a backlight module is disposed behind the liquid crystal panel and used as a flat surface light source of the liquid crystal panel. The optical quality of the flat surface light source greatly affects the display quality of the LCD. For example, in order to make the display image to be correctly displayed and have little distortion, a uniform flat panel light source is needed. Moreover, in order to improve the brightness of the display image, the range of the light emitting angle of the flat panel source may also be limited to avoid the lose of the light.
A conventional side type backlight module has a light guide plate, besides, a lower diffuser, two prism sheets with prism rods perpendicular to each other, and a upper diffuser are arranged on the light guide plate in sequence from down to up, wherein the prism sheets are used to minimize the range of the light emitting angle, also the upper diffuser and the lower diffuser are used to make the light uniform and to avoid producing moiré between the outline of the prism rods and the liquid crystal panel. However, the method of disposing four optical films on the light guide plate may increase the cost of the backlight module and too many optical films may make assembly difficult and be difficult to reduce the thickness of the backlight module.
In addition, the Taiwan patent publication number 200911513 discloses an optical film structure disposed on the light guide plate. The optical film structure has a light transmissive body and a reflective layer disposed on the light incident surface of the light transmissive body, and a lens array is disposed on the light emitting surface of the light transmissive body. Moreover, an opening corresponding to the lens is disposed at the reflective layer. In addition, the American publication number 20070002452 also discloses the same type optical film structure. However, to the different demands of brightness distribution at different angles in different directions, the backlight modules of the liquid crystal display of different electronic equipments (such as mobile phone, notebook computer, monitor TV and other liquid crystal display) using the optical film structures of the two above mentioned patent have difficulty to make the range of the light emitting angle change with the changing of the direction, so the design concepts of the mentioned patents above are difficult to apply to different kinds of electronic equipments at the same time.